Yo he hecho esto y funciona sin problemas y se mantiene en el tiempo.
[HKEY_LOCAL_MACHINE\Software\Microsoft\RIL\Operator Names]
but there is some funky stuff you need to do to add the key, you need to find your MNC (Mobile Network Code) and MCC (Mobile Country Code) and add these 2 numbers in a registry key.
Get Your MNC & MCC Here
I am in the UK, on O2, my current carrier name is "O2-UK"
For UK-O2:
MCC = 234
MNC = 02 or 10
Combining these gives: 23402 or 23410
Also i want to change the "O2-UK" to "Unknown Network"
Then make the following edit (These are strings (Reg_SZ in taskmanager) NOT DWORD!!):
[HKEY_LOCAL_MACHINE\Software\Microsoft\RIL\Operator Names]
"23410"="Unknown Network"